1. Field of the Invention
The present invention relates to a rotatable connector for electrically connecting an electric part such as an air bag inflator mounted on a steering wheel of an automobile to a steering column side, and more particularly to a rotatable connector having a turning angle detecting function for detecting the turning angle of the steering wheel.
2. Description of the Prior Art
Generally a rotatable connector is mounted, between the steering wheel and steering column of the automobile, for electrically connecting a horn switch and an air bag inflator installed on the steering wheel to the steering column side. Recently, however, there has been adopted such a system that the turning angle of the steering wheel is detected by an angle sensor, and the damping force of the suspension and the shift position of an automatic transmission are controlled in accordance with information on turning from the angle sensor.
There has been known an assembly structure including an outer rotatable connector and an inner angle sensor which are both assembled in one body and arranged around the steering shaft. In this case, the rotatable connector is of such a structure that spiral cables are housed in a pair of casings; a rotating casing is connected with a rotor member which rotates integrally with the steering shaft, while a stationary casing is fixedly attached to a stator member of the steering column. The angle sensor consists of a resistance contact type rotary encoder; the moving plate thereof is formed integrally with the rotating casing of the rotatable connector, and the stationary plate is formed integrally with the stationary casing of the rotatable connector. Therefore, as the steering wheel is turned, the rotating casing of the rotatable connector and the moving plate of the angle sensor also turn in synchronization with the steering wheel, thereby maintaining electrical connection by the rotatable connector between the steering wheel and the steering column and further enabling detection of such information on turning as the turning angle and direction of the steering wheel by means of the angle sensor.
According to the above-described prior art technology, the angle sensor and the rotatable connector are arranged concentrically around the steering shaft, and therefore the rotatable connector can be reduced in thickness more than the prior art in which the angle sensor and the rotatable connector are stacked along the axial direction of the steering shaft. Contrarily, however, there exists such a problem that the size in the diametral direction increases. Furthermore, the angle sensor and the rotatable connector are integrally assembled as a single assembly structure; however, before thus assembling into one body, the angle sensor and the rotatable connector are manufactured separately and therefore the number of component parts will increase, resulting in a complicated structure.